Detection and avoidance of obstacles is a primary function of any transportation device operator. Airborne transportation device operators, in particular, must be acutely aware of obstacles in their proximity. Without defined obstacle-free transportation channels—such as roads and shipping lanes—the potential for collision in an airborne transportation device is substantially greater.
There are numerous accidents each year where a helicopter strikes an electrical power line. Because power lines can quickly entangle and ensnare a helicopter's rotors, these accidents are often fatal. These accidents can occur on helicopter Emergency Medical Service flights, where the pilot is typically navigating an unfamiliar landing zone. These accidents also occur at night, even on very routine flights, where the helicopter operator suffers a momentary lack of situational awareness.
There are many solutions to avoiding power lines and other obstacles. The basic solution is a “see-and-avoid” approach—the operator sees the power line or other obstacles and takes the necessary evasive maneuvers to avoid a collision. This solution is critically dependent on a number of factors: the operator's ability to make reliable visual contact with the obstacles, the operator's alertness, and the operator's competence.
Recognizing the limits to the see-and-avoid approach, some helicopter manufacturers equip their airframes with “wire cutters” or other sharp blades that protrude from the top and bottom of the aircraft. The wire cutters are intended to cut the power lines before the lines can damage or entangle the helicopter's rotor system. This solution is oftentimes ineffective when the cutters are not properly positioned to engage the power lines and, when effective, can cause significant damage to electrical infrastructure.
U.S. Pat. No. 6,002,348, assigned to Safe Flight Instrument Corporation, the disclosure of which is incorporated by reference herein in its entirety, teaches an airborne power line detector and warning system which includes a low frequency radio and antenna for detecting an AC signal of about 50 to 60 hertz, that is, the oscillating frequency of electric current in the United States and Europe. The system provides an audible alarm to alert the pilot to power lines in proximity to the device. Optical laser-based systems have also been developed for detecting obstacles in proximity to the device, including power lines.
More generally, Terrain Awareness and Warning Systems (“TAWS”) and Enhanced Ground Proximity Warning Systems (“EGPWS”) provide limited alerts to transportation device operators for potential collisions. These systems employ a positioning system, an obstacle coordinates database, and a visual display. The positioning system identifies the coordinates of the transportation device, which are then correlated with the obstacle coordinates database to establish a set of obstacles in proximity to the device. The visual display renders a depiction of the obstacles in proximity to the device and their relative positions to the transportation device. Some TAWS and EGPWS combine the transportation device's altitude—obtained through a barometric or radar altimeter—with the set of obstacles in proximity to the device to determine the potential for collision and notify the operator when the probability of a collision exceeds a predetermined threshold. For example, if the transportation device's altitude is lower than the elevation of an obstacle in proximity to the device, the system alerts the pilot that an evasive maneuver is necessary. An example of such a system is the “MK XXII Helicopter Enhanced Ground Proximity Warning System” manufactured by Honeywell International, Inc. The efficacy of such systems, however, is dependent on the accuracy of the data in the obstacle coordinates database.
TAWS may be enhanced for helicopter operators. An example is the HeliTAWS™ system manufactured by Sandel Avionics, Inc. In these systems, the obstacle coordinate database has been expanded to include the location of known power lines. The power lines are then depicted on the visual display to improve the pilot's situational awareness. These systems prove ineffective when the coordinates of the power lines are not entered correctly, where new power lines are installed after the last revision to the obstacle coordinates database, or where power lines have been relocated since the last revision to the obstacle coordinates database.